The present invention relates to a screen product, in particular suitable for use in flat screen or rotary screen printing, comprising an electroformed, essentially nickel-containing metal body which determines two essentially parallel faces, and which is provided with a large number of openings, each opening extending from one of the two faces to the other, and each opening having a side wall in common with the metal.
Such a screen product is known and, as already mentioned, is used in particular in flat screen or rotary screen printing. Such a screen product is usually manufactured from nickel which has been formed by the electroforming process. The screen product is a flat screen or a cylindrical screen, depending on its application. In order to use the screen product in screen printing, a photosensitive lacquer composition is generally applied in a known manner to a face of the screen product and is subsequently irradiated patternwise. This patternwise irradiation can be carried out by means of a radiation source, for example a laser beam which is directed at right angles to the face with the photosensitive lacquer composition and is moved along it according to a pattern.
Another possibility is to place a mask over the coating of photosensitive lacquer, following which the photosensitive material not covered by the mask is irradiated. The irradiation is generally followed by a conventional developing operation in which, for example, the exposed parts of the photosensitive material are removed, while the unexposed parts remain behind on the material. Thus a screen product is obtained which is provided with a sealing pattern while--partially--leaving clear the openings through which in a printing operation printing paste is conveyed from one side of the screen product to the other side, in order to be deposited subsequently on a substrate material which is in contact with the screen product.
The abovementioned screen product must have such surface properties that the photosensitive materials used show excellent adhesion to the side of the screen product which during the printing process is in contact with the substrate material to be printed. In the case of the conventional screen products the adhesion with the conventional photosensitive materials is excellent.
It has been found that during--patternwise--exposure of the photosensitive lacquer material the radiation which penetrates to the surface of the screen product is largely reflected in different directions by said surface. As a result of said reflection (light scattering) of the radiation, parts of the photosensitive lacquer composition which should not have been exposed, for example because they were covered by a mask, are now in fact exposed, and consequently affect the predetermined pattern. The result of this is that the edge definition of the photosensitive material after the developing process is lower than would be the case without the occurrence of light scattering, and the consequence is that the pattern to be printed is of lower quality as regards fineness, smoothness, edge definition and edge shape than was intended.
A method is disclosed in U.S. Pat. No. 3,808,751 for making a mask or selective sand blasting of the substrate wherein a light absorbing filter layer is applied to the substrate and subsequently a photosensitive layer is formed on the filter layer. The photosensitive layer is exposed to light through a photomask and developed in the usual manner. Thereafter, the substrate is sand blasted through the sand blasted mask thus obtained in order to remove material from the substrate. The function of the light absorbing filter layer is to reduce the deterioration of the pattern formed from the photosensitive layer, which deterioration is caused by light scattering from the surface of the substrate.